"'Yeah, it's no big deal,' he said casually. 'The main thing I have is this thing called man-bi-du-lo-facial dys-os-tosis – which took me forever to learn how to pronounce, by the way. But I also have this other syndrome thing that I can't even pronounce. And these things kind of just morphed together into one big superthing, which is so rare they don't even have a name for it. I mean, I don't want to brag or anything, but I'm actually considered something of a medical wonder, you know.'

He smiled.

'That was a joke,' he said. 'You can laugh.'"

It is curious how the gravity of serious subjects can be best expressed through humour. Comedy humanises: the light touch gives weight. It's a tactic RJ Palacio has used to great effect in her remarkable story of a year in the life of 10-year-old August Pullman, a boy without a "normal" face. "I won't describe what I look like. Whatever you're thinking, it's probably worse." As the book opens, he has just agreed – after years of home-schooling and despite his understandable anxiety – to attend a regular school.

There are enough novels describing the experiences of the severely disadvantaged to make the inevitable storyline immediately apparent. After encountering ignorance, discrimination and hostility, the sweet-natured Auggie will gradually win sympathy and acceptance, and ultimately triumph over circumstances. Wonder does not depart from this basic model. All the more impressive, then, that it finds ways to make the story hugely compelling as well as moving. It makes ordinary things extraordinary. Simple events of the school year – Halloween, science projects, an outward bound trip, an end-of-term show – become unpredictable dramas, some desperately upsetting, some triumphantly joyful. But more striking still, it makes the extraordinary ordinary again, allowing the "Freak" to become Auggie Pullman, a kid at a school.

There are technical reasons for this success. The radically short chapters – many shorter than paragraphs in other books – inject speed into the narrative and keep the focus on telling incidentals. The decision to tell the story from the perspectives of several characters opens up startling new views on Auggie and shifts him from centre stage to where he much more interestingly belongs – among his peers. It's a pity, perhaps, that Palacio didn't give voice to Auggie's worst tormenter, the stuck-up bully Julian Albans, but there are terrific contributions from Jack, who has problems becoming Auggie's best friend; Via, Auggie's older sister, struggling with her first year of high school; and Miranda, Via's ex-best friend, who has powerful but barely understood feelings for Auggie. Each account is different but all are vivid. Palacio has a great ear for dialogue, a sharp eye for detail and an instinctive sense of comedy. All this makes her an expert chronicler of ordinariness – and this, paradoxically, is what makes her story of an extraordinary boy so wonderful.

There is didacticism – perhaps inevitable – popping up in the quotations that open the sections and in the "precepts" of Mr Browne, the popular English teacher ("Your deeds are your monuments"), but it is done with a light touch. Wonder certainly delivers what it promises – an emotional roller-coaster ride in which tears, laughter and triumphant fist-pumping are mandatory. But it is better than that. In its assured simplicity and boldness (reminiscent – it seemed to me – of To Kill a Mockingbird), it also has the power to move hearts and change minds.